Printing systems such as stencil and screen printing systems find wide use within the electronics industry. Such systems are typically used to apply conductive print substances over a substrate, such as to form current carrying conductive interconnect lines on printed circuit boards. Such systems are also used in flip-chip bonding. Here, bumps of solder or other conductive material are deposited onto conductive pads of a semiconductor wafer or chip. After separation of individual dies from the wafer, the individual dies or chips are turned upside down, and the bumps are properly aligned with a metallization pattern on another substrate. The aligned bumps are then joined to appropriate points on the pattern.
One problem which is associated with such printing systems relates to an inability to achieve adequate print substance separation from its associated print system when a particular substrate is printed upon. An exemplary manifestation of this problem is in the context of flip chip bonding with a stencil printing system. A stencil printing system typically includes a stencil having number of perforations or apertures through which conductive material is provided to a substrate. The aspect ratio relative to such perforations, e.g., the thickness of the perforated print device immediately adjacent the perforation divided by the aperture opening size of the perforated print device, along with the physical characteristics of the print substance material, can affect the amount of material and the adequacy with which such material is formed onto a substrate. As an example, consider formation of conductive bumps having a height of around 7 mils and a width at the base of around 12 mils. Such would require a stencil having perforations with aspect ratios of no less than, and possibly greater than 0.58. Yet, such aspect ratios have been problematic in achieving adequate, standardized and repeatable flip chip bump configurations. This is believed to be due in part to the inability of the print substance to pull cleanly from the stencil apertures when the stencil is separated from the substrate.
This invention arose out of concerns associated with improving the methods and systems by which print substances are rendered onto substrates, and more particularly with enabling higher aspect ratio conductive features to be printed on substrates.